The invention relates generally to electromagnetic synchronizers and brakes for motor vehicle transfer cases and more particularly to an electromagnetic synchronizer and brake for the input and secondary output of a motor vehicle transfer case having an interaxle differential.
Many four-wheel drive motor vehicles and sport utility vehicles or pick-up trucks equipped with four-wheel drive utilize a transfer case coupled to the output of the transmission to distribute drive torque to the front and rear axles of the vehicle. These transfer cases incorporate many diverse mechanical devices which may provide, among other features, a reduced speed (low gear) drive mode, interaxle speed differentiation and manual or automatic engagement of an interaxle clutch which selectively reduces prop shaft speed differences or positively drives both front and rear prop shafts.
Significant developments have been made with regard to systems which sense wheel speed differences and engage interaxle clutches to reduce such speed differences. An automatically engaging system is disclosed, for example, in co-owned U.S. Pat. No. 5,407,024.
In addition to developments directed to enhancing the flexibility and operation of such drive system are developments directed to providing smooth, silent and imperceptible operation of the vehicle drive system under all operating conditions.
One condition that has recently been subjected to scrutiny is the clunk or thunk which occurs when the vehicle driveline suddenly changes state from driving or accelerating to coasting. During this change, the direction of rotational clearances in the driveline components is reversed and the shift of the accumulated slack or lash frequently results in a clunk or thunk. In severe cases, a slight impulse or lurch is transmitted to the vehicle body and its occupants. The present invention is directed to this problem.